This invention relates generally to a speed changing device having a driver and a driven pulley different in diameter from each other and being coupled with an endless member so that the input rotational speed provided by a motor is changed, and thus, a different output rotational speed is provided. More specifically, the invention relates to a structure which allows various pulley sizes to be replaced and used so that a desired increase or decrease in the rotational speed can be attained. The structure further provides for the adjustment of the distance between the driven and driver pulleys so that the tension of the drive belt can be adjusted.
Variable speed electric motors are generally very expensive compared to single constant speed electric motors. Further, in many applications, only a single different rotational speed than that of a constant speed motor is desired. Accordingly, there is a need for a mechanism to decrease or increase the output rotational speed of a constant speed motor. Often, the output speed must be reduced and the power increased while on other occasions the rotational output speed must be increased and the power decreased accordingly. Further yet, there is a need for the speed changing mechanism to provide for a range of decreasing or increasing speed ratios with the same mechanism, and it is highly desirable if this can be accomplished by replacing only a minimum number of parts.
In the past, speed changers have utilized primarily gear mechanisms. Gears, however, are very expensive, noisy, require maintenance in terms of lubrication and tend to wear quickly. Further, gear mechanisms do not provide a means for easily changing the output speed because it is costly and generally difficult to retain the tolerances required when replacing gears so as to make them mesh properly. There is, therefore, a need for a speed changing mechanism which substantially overcomes the disadvantages associated with gear changing mechanisms.
Many disadvantages associated with gearing can be overcome by utilizing pulleys and drive belts. Various pulley sizes can be selected and coupled together with a drive belt so that a different rotational speed output can be attained. Thus, there is a need for a speed changing device wherein only the pulleys and drive belt can be changed and therethrough different output speeds can be obtained.
However, there is also a need for a structure whereby the tension of the drive belt can be adjusted for any combination of pulleys while using the same speed changing device. The structure used to provide the tension adjustment needs to be easily accessible and easily used through the use of conventional tools. The adjustment structure should also provide for an infinite number of settings within the ratio range so that the tension of the drive belt can be adjusted to an infinite number of settings. Upon attaining the desired tension, there is also a need to fasten and hold in position the previously set tension adjustment during the operation of the speed changing mechanism.
Overall, there is a need to make the structure for adjusting and retaining the tension in the drive belt strong and capable of withstanding the forces exerted upon it while still being cost efficient. Further yet, the adjusting structure must provide a way for easily adjusting the tension of the endless member after it has been in operation for a period of time.